Covid-19: 50% global reduction in seismic noise during lockdown

The coronavirus-induced lockdown has brought the world to a standstill. Human activity in the urban areas was reduced to the least as regulations barred people from stepping out of their houses. The reward was cleaner air and clearer skies.

READ: Air quality improved due to COVID-19 lockdown: CPCB

Today, as countries look forward to reboot their economies while fighting against the health crisis, researchers noted a significant 50 per cent drop in human-linked vibrations within the earth between March and May 2020.

New research led by the Royal Observatory of Belgium and five other institutions around the world including Imperial College London found that owing to the total global effect of social distancing measures, closure of services and industry, and drops in tourism and travel, the lockdown period was the longest and most pronounced quiet period of seismic noise in recorded history.

The study was conducted through a global network of 268 seismic stations in 117 countries. It established significant noise reductions compared to before any lockdown at 185 of those stations.

Human and natural seismic noise

Seismic noise — caused by vibrations within the Earth — is measured with seismometers. The seismic waves can be triggered by earthquakes, volcanoes, and bombs. However, daily human activities like availing transport services and operating industries, primarily in densely populated areas, also cause seismic waves beneath the surface of the earth.

It was difficult for scientists and researchers to differentiate between the human and natural seismic noise that might warn of upcoming natural disasters. The paper stated that earlier, the human-generated seismic noise or ‘anthropogenic noise’ was recorded the lowest during weekends, holidays and nights.

But during the lockdown period, the drop in the human seismic noise was dramatically higher than ever recorded.

As a consequence, the paper states, although there was no reduction in earthquakes in 2020, the ‘relative quietness’ during the lockdown period allowed researchers to listen in to previously concealed earthquake signals.

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Importantly, it also helped them to differentiate between human and natural seismic noise more clearly than ever before.

One of the authors of the study wrote, "With increasing urbanisation and growing global populations, more people will be living in geologically hazardous areas. It will, therefore, become more important than ever to differentiate between natural and human-caused noise so that we can 'listen in' and better monitor the ground movements beneath our feet. This study could help to kick-start this new field of study."